Field of the Invention
The present invention concerns a high speed synchronous machine, preferably a motor, comprising a rotor constituted by permanent magnets the magnetic induction of which is tangential or orthoradial and by pole-pieces deviating this magnetic induction of the permanent magnets in order for said induction to be radial at the periphery.
A synchronous motor comprises a multiphase stator and a rotor provided with permanent magnets. The stator is supplied with a multiphase alternating current that generates a rotating field causing the rotation of the rotor.
For the manufacture of such rotors, use is increasingly being made of rare earth magnets, especially samarium-cobalt magnets, for example, SmCo.sub.5, which present a low demagnetizing rate as well as a high magnetizing energy per volume unit, thereby allowing to obtain high mass torque motors, i.e. motors with a high torque in relation to a small mass. The drawback of such magnets is, however, that they present a relatively low remanent induction. This is the reason why these magnets are conventionally disposed in such a way that their magnetization is orthoradial and are associated to pole-pieces adapted to concentrate the flux, thereby allowing to confer upon the induction the radial direction in the air-gap. In this way, the two poles of each magnet are fully utilized.
This heterogeneous structure of the rotor raises mechanical cohesion problems that are more difficult to overcome as the speed of rotation increases. In order to improve this cohesion at very high speeds, of about 50 000 rpm, French patent published under No. 2 519 483 proposes a laminated rotor formed of a staggered stack, in the axial direction, of nonmagnetic disks for maintaining the magnets and which are crossed through by these magnets and magnetic plates in contact with the magnets, this stack being maintained in radial direction by bars crossing through the plates and the disks. Furthermore, in the rotor described in the above-mentioned French patent, each pole-piece between two adjacent magnets comprises two portions, the separation line running in the radial direction, and prestressed means are disposed between the two half pole-pieces so as to urge each of them against the corresponding magnet.
This rotor, which is particularly well adapted to high speeds, has, however, a complicated form and is expensive to produce.